Tag Archives: GFS

On Friday, I wrote about the possibility of the season’s first hurricane developing from a tropical wave that was about to emerge from the coast of Africa. At that point, two of the major global computer models, the GFS and ECMWF, were both indicating the development of the tropical wave as it approached the Lesser Antilles.

Now, here we are on Monday and the GFS essentially stands alone. The ECMWF has all but completely dropped the notion of development while the GFS is about as consistent as it can be.

If we follow the evidence we can try to figure out what may end up happening – while also either confirming or denying the GFS and its ability to forecast the development of a tropical storm in the deep tropics.

I have prepared a video discussion covering this intriguing situation by taking a close look at not only the model forecast but also what we see in front of us right now. What does the evidence show? Is there enough there to support the idea of a tropical storm forming later this week? Check out the video below to learn more.

Graphic from Colorado State University’s July hurricane season forecast outlook showing the below avg wind shear (blue color) across the MDR for the month of June. Click for full size.

The update from Colorado State University to the 2017 Atlantic hurricane season forecast made mention of the fact that, during the month of June, sea-level pressures were well below average across the deep tropics – also known as the MDR or Main Development Region. This is the area between Africa and the Lesser Antilles and has seen its share of powerful hurricanes over the decades.

In recent years, however, the MDR has been notably quiet. Dry air, strong upper level winds and generally higher than normal pressures have kept the region much more benign – resulting in far less hurricanes such as what we saw in 2004 with Frances and Ivan, as examples.

This year, it is becoming more and more obvious that the sleeping giant is awakening, so to speak. Water temps across the MDR are above normal, wind shear is below normal and surface pressures are below normal. The result thus far has been the formation of tropical storm Bret last month (extremely rare to have MDR tropical storms in June) and now, most recently, tropical depression four – technically a tropical cyclone though below tropical storm intensity. The only significant mitigating factor keeping TD4 in check has been a large Saharan Air Layer or SAL event that has pushed ample dry air in to the deep tropics, smothering the depression and keeping it from strengthening further. This SAL outbreak is typical for July, having a tropical depression in the MDR is not.

ECMWF model at day 5 from last night’s run showing energy or vorticity at the 850mb level of the atmosphere (circled in green). Image courtesy of Levi Cowan – tropicaltidbits.com. Click for full size image.

Now comes the next chapter in this story. Both the GFS and the ECMWF are now indicating the development of a tropical storm originating from a tropical wave that is about to emerge from the African coastline. I want to be clear, the development happens beyond the 5-day time frame but well within the next 10 days. Since both of these global models now indicate this happening, it has my attention. In fact, both models go on to develop the system in to what would likely be a hurricane later on in their forecast periods but again, not at some ridiculous time frame such as 10 to 14 days out – what many consider to be “model fantasyland”.

What concerns me about this is the mere fact that it is still early July, several weeks ahead of the traditional beginning to the normal run-up to the peak of the season and we’re talking about yet another MDR system trying to develop. In other words, if it’s this busy now, when climatology says it should not be, how busy will it be when the natural background state is inherently favorable? That usually sets in around August 15-20 and lasts until the end of October.

I make it a point to refrain from being an alarmist – those who have followed my blogs and video discussions know this and I stand firm behind that belief. At this point, I am beginning to worry that this season could end up exceeding all of our expectations in a bad way. The time-tested saying of “it only takes one” remains intact but this is the kind of season where we could be looking at multiple “it only takes one” events. Please keep in mind too that I am not talking about just the United States in terms of impact. The Lesser Antilles are front and center for any action that rolls out of the MDR and west of there we have Puerto Rico, Hispaniola and Cuba. This is the kind of season that could affect a lot of people across the Atlantic Basin and in areas that can least afford such bad luck.

I am going to say it, the signs are ominous right now. We’ve gone a long time without experiencing a category three or higher hurricane in the United States. They’ve also been somewhat rare elsewhere with the exception of Matthew and its devastating impacts on Haiti, eastern Cuba and the Bahamas last year (Joaquin in 2015 also impacted portions of the Bahamas). It is time to take notice and be ready to act.

Needless to say I am going to be watching the evolution of this next potential system very closely over the coming days. Perhaps it is just a blip in the models and subsequent runs will drop the storm/hurricane completely and we can all breathe a sigh of relief. I will post a detailed video discussion concerning this potential development later this afternoon once the morning model runs complete and are available.

It’s still early June and typically this time of the hurricane season means that things are usually quiet. Every once in a while we will get a June tropical storm or hurricane, but it’s not the norm. As most of you know, the season really begins to ramp up from about mid-August on. Usually….

This season might not be usual.

I am seeing the beginnings of signs that may point to a development window opening over the next week to ten days and beyond.

GFS and its ensemble members indicating a more favorable MJO state coming up for portions of the Western Hemisphere over the next couple of weeks

For starters, the Madden-Julian Oscillation or MJO is forecast by the GFS and Euro models to be moving in to the phase that often supports development somewhere within the Atlantic Basin. The MJO phenomenon is easy to think of as a period of fertility in the tropics, when deep convection can form and blossom, not just fizzle out and dissipate. While the MJO helps to enhance development it does not necessarily mean that development is a certainty.

The upcoming signal from the MJO is not especially strong but it is there (forecast to be there anyway) and could lead to better upper level winds over parts of the southeast Pacific and extending in to the western Caribbean and western Gulf. With water temps plenty warm in the region, all we need is a kick and it could lead to development in one basin or the other, maybe both. We will have to just wait and see.

If we look at the GFS operational model at the 850 millibar level which is about 5k feet up, we can see one week out from today that a wind shift or monsoonal trough begins to set up from the southeast Pacific, across Central America and in to the western Caribbean. This would act like a focusing mechanism for the air to come together or converge, probably leading to enhanced convection (thunderstorms) across the region.

GFS model at 168 hrs showing (yellow area) a wind shift and overall troughof low pressure stretched out over a large area, we call this a “monsoon trough” and it can lead to development if conditions allow

This large counter-clockwise “gyre” is so spread out that in and of itself it wouldn’t develop. We would need to see if an area of concentrated energy or vorticity breaks off and tries to develop out of this larger area of energy. If so, then a low pressure area could get going either in the Pacific or the western Caribbean – leading to the chance of a tropical depression or storm at some point.

As you can tell, the process is long and complex. I am not going to dwell on it day after day for two weeks but it is something to keep an eye on. At the very least, more rainfall than normal may be setting up for portions of Central America and it may lead to a named storm on one side of Central America or the other. Time will tell.

Then there is this interesting set up taking shape: The ECMWF (Euro) is indicating the possibility of an easterly wave (tropical wave) trying to develop way out in the deep tropics between Africa and the Lesser Antilles. Remember, water temps out this way are running above the long term average. If we do in fact see a strong area of energy emerge from Africa, it could take advantage of the warmer water and more favorable conditions overall and try to develop some. This would be highly unusual and a significant sign in my opinion that this season could be quite busy. Again, time will tell.

We live in an age when computer guidance and satellite information allows us to see in to the future of weather forecasting better than ever before. These early warning signs are helpful since we should no longer be totally caught off guard. It may not prevent a “Labor Day hurricane of 1935” scenario in which case we saw a TS become a Cat-5 hurricane in a very short amount of time but the advances in technology now allows us to be more aware than ever that a threat from the tropics is looming (or could be looming). My point is, do not be alarmed or worried. There’s no reason for that. Instead, be aware. We were told the season could be busier than average and these are possible signs of that happening. So just take note and pay attention a little more than normal perhaps. Applaud the fact that we have such tools at our disposal and as long as we know how to interpret them, it can be a good thing. After all, with such much at stake along our coastlines (all of us, not just the USA), the more lead-time the better; at least I think so anyway.

Recent visible satellite image of Matthew. Notice the clearer eye now, it had been clouded over earlier in the morning.

The latest update from the NHC now indicates a hurricane watch for two areas in the Caribbean Sea: all of Jamaica and the western portion of Haiti. This means that hurricane conditions are possible in the watch area within the next 48 hours or so.

Matthew continues to move slowly west with winds of 145 mph. Some westerly shear has impacted the circulation and caused the hurricane to weaken overnight from its incredible peak of 160 mph. As of this writing, the eye seems to be clearing out again meaning that perhaps some slight re-organization is taking place but these ups and downs are to be expected, especially with exceptionally strong hurricanes. It is likely that Matthew will be a strong hurricane as it approaches Jamaica and western Haiti on Monday.

Interests in the two island regions need to be preparing for a hurricane at this time. Heavy rain, which will surely lead to flash flooding and mudslides in the mountains of the two countries, along with dangerous seas and high winds will be the expected impacts. To what extent each of these hazards will affect the area remains to be seen. We will know more tomorrow as Matthew gets closer and we can see how strong and well organized it is. Obviously the closer the core tracks to either location, the more pronounced the effects will be.

Next up will be a landfall in southeast Cuba along the Caribbean coast. The mountain range that runs east-west across Cuba at that latitude will disrupt the circulation of Matthew some but it is forecast to reach category three intensity once again over the very warm waters of the southwest Atlantic.

The next few days are fairly certain in terms of the forecast track for Matthew. It’s what happens after Cuba that has tremendous uncertainty. Essentially it’s another duel between the GFS global model and the ECMWF global model with other models picking sides either way. Instead of trying to figure it all out with lengthy explanations of why one model shows this and why one shows that I want to set a benchmark – point in space and time to watch for.

If Matthew goes over Jamaica, the center of the hurricane that is, then the GFS seems to have the right forecast so far. If it goes over Haiti, then the latest runs of the ECMWF are doing better. We will absolutely know the “winner” by Monday. It’s that simple in terms of the short-term (3-day) window of which model is performing best on track. From there, we will have ample time to prepare in the Bahamas and the United States as needed.